Although older people are more likely to be lonely and face a higher mortality risk, the association between loneliness and risk of mortality among the young population is actually greater than among the older population, the researchers noted.

Loneliness and social isolation better predict premature death among a population younger than 65 years, they added.

The study analysed data from a variety of health studies. Altogether, the sample included more than three million participants from studies that included data for loneliness, social isolation and living alone.

"In essence, the study is saying the more positive psychology we have in our world, the better we're able to function not just emotionally but physically," co-author of the study Tim Smith from the BYU noted.

Loneliness and social isolation can look very different. For example, someone may be surrounded by many people but still feel alone. Other people may isolate themselves because they prefer to be alone. The effect on longevity, however, is much the same for those two scenarios, the study pointed out.

The study appeared in the journal Perspectives on Psychological Science.